Cam operated clutches with automatic lock

ABSTRACT

This invention relates to actuators incorporating a drive mechanism by which an output member is selectively operated either manually by rotation of a handwheel or by power means such as an electric motor. According to the invention the drive mechanism includes a clutch member slidably, but non-rotatably, mounted on the output member for movement in one direction to engage the handwheel and in the other direction to engage the power means. The clutch member is movable in one direction by a lifting jack against the action of a spring. One of the co-operating surfaces of the lifting jack and the clutch member is formed as a cam surface which is so shaped that the resulting force on the clutch member is always at a constant angle relative to the centre line of the clutch member and is always within the length of the clutch member.

I United States Patent 1191 1111 3,863,745

Fry Feb. 4, 1975 [541 CAM OPERATED CLUTCHES WITH 3.603.175 9/1971 Horton 192/114 x AUTOMATIC LOCK [75] Inventor: Jeremy Joseph Fry, Bath, England Primary Emmm"Benjamin wyche A Attorney, Agent, or Firm-Clelle W. Upchurch [73] Assignee: Rotork Llmlted, Lower Weston,

Bath, Somerset, England [22] Filed: Mar. 9, 1973 [57] ABSTRACT This invention relates to actuators incorporating a [21] Appl' 339312 drive mechanism by which an output member is selectively operated either manually by rotation of a hand- [30] Foreign Application Priority Dat wheel or by power means such as an electric motor.

Mar. 23, 1972 Great Britain 13630/72 According to the invention the drive mechanism includes a clutch member slidably, but non-rotatably, [52] U.S. Cl. 192/93 R, 64/016. 2, 74/625, mounted on the output member for movement in one 192/114 R, 192/48.91, 192/150 direction to engage the handwheel and in the other [51] Int. Cl. Fl6d 11/04 direction to engage the power means. {58] Field Burch 14 R1 99 93 The clutch member is movable in one direction by a 92/89 74/625 lifting jack against the action of a spring. One of the co-operating surfaces of the lifting jack and the clutch [56] Rehrencgs cued member is formed as a cam surface which is so shaped UNITED STATES PATENTS that the resulting force on the clutch member is 2,551,922 5/1951 Av 192 394 always at a constant angle relative to the centre line of 3,198,033 8/1965 Fry 192/114 R X the clutch member and is always within the length of 3,234,818 2/1966 Cantalupo et a1 192/114 R X the clutch member. 3,257,866 6/1966 Fry 74/625 3,383,948 5/1968 Palmer et a1 192/114 R X 10 Claims, 4 Drawing Figures 1 78 -66 l 63-175 72 I q 70 79 32 1 l 84 V 1 7J1; T5 I J CAM OPERATED CLUTCHES WITH AUTOMATIC LOCK This invention relates to actuators of the kind (hereinafter called the kind referred to) incorporating a drive mechanism by which an output member may be selectively operated either manually, i.e., by rotation of the customary handwheel or by power means, such as an electric motor.

In known arrangements of such actuators a clutch member is provided which is movable axially, for example by a hand lever, in one direction to couple the output shaft to the handwheel for manual operation. The clutch member is automatically moved, for example by a spring, to reset the actuator for power operation upon energization of the electric motor which causes the disengagement of retaining means normally holding the clutch member in driving engagement with the handwheel.

The invention is particularly concerned with actuators in which the clutch member comprises a ring or sleeve slidably but non-rotatably mounted on the output shaft of the actuator. The clutch sleeve is movable axially to engage drivably with the handwheel by means of a manual mechanism which is operable to lift or otherwise move the clutch sleeve against the action of resilient means, and which holds the clutch sleeve in driving engagement with the handwheel by means ofa pawl or finger which is mounted on the manual mechanism. The pawl or finger engages a fixed member which is conveniently a movable part of the power drive means, for example a drive pinion or wormwheel so that the pawl or finger and thereby the handwheel is automatically disengaged from energization of the power means.

The object of the present invention is to provide a greatly improved and more efficient pawl or finger assembly which is in the form of a hand/auto jack which is operable by the manual mechanism to push directly on the centre line of the clutch sleeve so as to lift against the clutch spring.

According to the invention the finger or pawl is mounted on a lifting jack which is manually operable for engaging and lifting the clutch ring or sleeve, the lifting jack being mounted on the inner end of a hand lever which extends into the casing of the actuator. One ofthe co-operating surfaces of the jack and clutch ring or sleeve is formed as a cam surface which is so sloped that the resultant force on the clutch ring or sleeve is always at a constant angle relative to the centre line of the clutch ring or sleeve and is always within the length of the clutch keys.

In one embodiment the sloped cam surface is formed on the clutch ring or sleeve. The pawl or finger in this embodiment preferably comprises a resilient stud carried by the lifting jack.

In a second embodiment the sloped cam surface is formed as a curved surface on the jack and engages the radiused underside of the clutch ring or sleeve. The pawl or finger is attached to the front end of a fulcrum pin which is located in a hole drilled in the lower part of the lifting jack. The fulcrum pin is provided with a pair of springs between the front face of the lifting jack and the pawl or finger. One of the springs is a helical compression spring which urges the finger or pawl forwardly so as to engage the upper surface of the wormwheel as the clutch sleeve or ring is lifted by the sloping cam surface of the lifting jack. The other spring is formed with two downwardly extending legs which by abutting a pin in the front face of the lifting jack and an extension to the pawl or finger, maintains the pawl or finger normally in a vertical position.

In order that the invention may be clearly understood embodiments of the improved actuator will now be described by way of example with reference to the accompanying drawings, in which:

FIG. I is a sectional elevation of a valve actuator taken on the line A--A of FIG. 2;

FIG. 2 is a sectional plan view of the actuator taken on the line 8-8 of FIG. 1;

FIG. 3 is an enlarged part sectional view of the manually operable lifting assembly for he clutch ring of the hand/auto mechanism; and

FIG. 4 is a sectional view of a modified manually operable lifting assembly.

The actuator 10 comprises a main casing or gear case II which is positioned substantially vertically. The lower part 12 of the casing l I is provided with an outlet 13 therein for the lower end of the main hollow output shaft 14 of the actuator which extends vertically in the casing 11. The lower end of the shaft [4 outside the casing II is provided with a combined radial and thrust bearing 15 which is capable of receiving thrust in response to movement of the output shaft 14 in either di' rection. The inner track 16 of the bearing 15 is trapped between a shoulder 17 and the outer sleeve 18 of a drive member 19. The sleeve 18 is threadably attached over the outer surface of the output shaft I4 and is formed with an internally extending end flange 20 which holds a nut member 2I in position inside the end of the hollow output shaft. The nut member is internally threaded or splined for engaging the valve spindle (not shown). The outer track 22 of the bearing 15 is trapped between the casing 10 adjacent the outlet 13 and a cover plate 23 which is directly attached to the casing II, for example by screws 24. The arrangement thus avoids the use of the usual thrust plate or base and the end loads applied by the valve through the bearing 15 can be taken directly by the casing 11 so long as the base of the casing is made sufficiently strong and rigid.

The hollow output shaft 14 is provided with an oil seal 25 in the output aperture I3 of the casing II and along its length within the casing II it is provided with a clutch member 26 which is slidably mounted on the shaft I4 for axial movement relatively thereto but which is keyed to the shaft so as to rotate therewith. As will be hereinafter explained the clutch member 26 is movable between two positions in one of which it connects the output shaft 14 with an electric motor 27 for power operation, and in the other of which it connects the output shaft I4 for manual operation by a handwheel 28 externally mounted on top of the casing II. The electric motor 27 for power operation is mounted in a horizontally located casing 29 extending from the main casing II to which it is connected by screws 30. The motor 27 is reversible and the driving shaft 3I extends through a wall 32 into the main casing 11, the other end 33 of the shaft 3i being provided with a worm 34 which is in driving engagement with a wormwheel 35 freely mounted around the hollow output shaft 14 and supported on a horizontal wall or plate 36. The worm 34 is of the threaded type and when operating the tangential load from the worm 34 tends to tilt the wormwheel 35 slightly which locks the wormwheel 35 in position on the hollow output shaft I4. The arrangement thus prevents the wormwheel from moving axially up the output shaft 14 and consequently it is not necessary to provide the usual position retaining plates for the wormwheel.

The opposite end 37 of the motor shaft 3l extends from the motor 27 into a small auxiliary housing 38 closed by an end cap 39 which positions a bearing 40 against the partition wall 4l. The bearing 40 supports the extension 37 of the motor shaft 3| which is of reduced diameter thus forming a shoulder 42. A disc spring pack 43 or helica spring is positioned between the shoulder 42 and the adjacent side of the bearing 40 and a second disc spring pack 44 or helical spring is positioned between the other side of the bearing 40 and a retainer 45 held on the shaft end by a nut 46.

The two springs 43, 44 act to centralise the motor shaft 3l while permitting axial movement of the shaft 31 in one or other axial direction depending on the direction of motor operation in response to a predetermined torque due to resistance to movement of the valve. This axial movement ofthe motor shaft 3] is normally used to operate torque switches in a control unit (not shown), for example, for de-energising the motor circuit. For this reason the end 33 of the motor or worm shaft 31 may be connected to an axially movable shaft 47 extending from the main casing into a control unit housing attached to the outlet 48. The control unit may be of the kind described in our U.S. Pat. No. 3,209,090 on Sept. 28. I965.

The clutch member 26 comprises a ring or sleeve 49 which is mounted within a pair of driving members or keys 50 of U shape (see FIG. I). The driving members or keys 50 are positioned diametrically of the clutch ring 49 and the base portion of each U-shaped driving member or key 50 is vertically positioned and slidably engaged within a vertical or axial keyway 51 (see FIGS. 2 and 3) in the surface of the output shaft 14. The upper horizontally extending arms 52 of the driving members or keys are each located in radial slots 53 in the upper surface 49' of the clutch ring 49 so as to prevent relative rotational movement (see FIGS. 1 and 2).

The clutch ring 49 is therefore slidably mounted for axial movement on the output shaft 14 by means of the driving members or keys 50 which are normally urged downwardly by a coiled compression spring 54 into engagement with the upper surface of the wormwheel 35. The wormwheel 35 is provided on its upper surface with driving dogs or projections 55 (FIG. 2) so as to impart the rotary movement of the wormwheel 35 to the output shaft 14 by engagement with the lower horizontally extending arms 56 of the driving members or keys 50 when the motor 27 is energised. When the actuator 10 is power operated generally some movement of the wormwheel 35 will occur before the driving dogs 55 engage the arms 56 driving members or keys 50 of the clutch member 26. The result is a hammer blow which frequently helps to free a stuck valve.

The upper end of the spring 54 acting on the clutch member 26 seats on a retainer 57 on the outer wall of the upper end of the output shaft 14. The shaft I4 is positioned within the hollow boss 58 of the handwheel 28 which is fitted directly into a top aperture 59 in the easing 11 and through which the mechanism is assembled. The handwheel boss 58 is retained in position in the aperture 59 by means of a long coiled spring 60 which seats in a groove formed partly in each of the adjacent surfaces of the handwheel boss 58 and the wall of the casing ll. The spring 60 is inserted through a hole drilled in the wall ofthe casing and retained by a screw which abuts the end ofthe spring where it emerges tangentially.

The lower edge surface of the handwheel boss 58 is provided with two diametrically positioned drive screws 61 on its lower edge surface and which are intended to engage drivably with the upper arms 52 of driving members or keys 50 of the clutch member 26 when the clutch member is slidably moved upwardly against its spring. When the clutch member 26 is held in its uppermost position rotation of the handwheel 28 will transmit rotation through the driving members or keys 50 and clutch ring 49 to the output shaft l4. As before this movement is generally preceded by an initial hammer blow. The movement of the clutch member 26 to its uppermost or manual position is obtained manually by the operator as will be hereinafter explained.

The mechanism for manually operating the clutch member 26 of the hand/auto mechanism is shown in FIGS. 2 and 3 and comprises a cranked hand lever 62 mounted externally of the actuator and forming part of a shaft 63 which is rotatably mounted in a machined bore 64 in a wall 65 of the actuator casing ll. The inner end of the hand lever shaft 63 extends into a chamber 66 formed in the casing ll and is located opposite the periphery of the clutch ring or sleeve 49.

The hand lever shaft 63 is held in position in the wall 65 of the actuator casing ll by means of a grub screw 67 adjusted externally of the casing and which is engageable with an annular groove 68 formed in the shaft 63. The shaft 63 is also provided with a suitable O-ring 69 for providing fluid tightness for the actuator casing ll.

The inner end ofthe hand lever shaft 63 has two flats 70,71 machined on its circumference. the flats being adjacent each other and located at a predetermined angle one to the other (see FIG. 3). A liftingjack 72 for moving the clutch ring 49 upwardly is positioned on the inner end ofthe hand lever shaft 63 at a position on the shaft which includes the two flats 70, 71. The lifting jack 72 comprises a member 73 of rectangular crosssection having a bore 74 of circular cross-section to accommodate the hand lever shaft 63. The lifting jack 72 is furthermore provided with a projecting arm 75, a top outer edge 76 of which is adapted to engage a cooperating surface 77 of the clutch ring 49 as will be hereinafter described.

The lifting jack 72 is provided with a transverse bore 78 extending across the circular bore 74 therein and which is adapted to receive a Mills pin 79 therein. The pin 79 extends across the section of the hand lever shaft 63 provided with the two flats 70, 71 and is engageable thereby for rotating the lifting jack 72 as will be hereinafter described The hand lever shaft 63 is completed by means of a return spring 80 which is positioned on the shaft 63 between the lifting jack 72 and the wall 65 of the casing ll, the spring 80 being connected to the wall 65 at one end and with the hand lever shaft 63 at the other end at a position adjacent the lifting jack 72. A washer 81 and retaining clip 82 are positioned on the inner end of the hand lever shaft 63 to complete the assembly.

The projecting arm of the lifting jack 72 supports a pawl or finger 83 which extends downwardly and which is preferably of a resilient construction. The pawl or finger 83 as shown comprises a coil compression spring having at one end a finger stud 84 for engaging the upper surface of the motor driven wormwheel 35 and at its other end a rigid connection for mounting in the arm 75 of the lifting jack 72.

As previously mentioned the upper outer edge 76 of the projecting arm 75 of the lifting jack 72 is adapted to engage a co-operating surface 77 on the clutch ring 49 which, as shown, is formed at an angle as a sloping cam surface. The sloped cam surface 77 of the clutch ring 49 is so angled that the resilient force Fl on the clutch ring 49 when the lifting jack 72 is rotated is always at a constant angle A relative to the centre line of the clutch ring 49 and is always within the length L of the clutch members of keys 50 so that the force vector intersects the shaft 14 at a point below the uppermost point on shaft 14, for example point X in the position of FIG. 3, within the length L of the clutch member to prevent jamming between the shaft l4 and the clutch member 26.

In the operation of the invention actuation of the hand lever 62 moves the lifting jack 72 so that its projecting arm 75 rotates upwardly in a clockwise direction as viewed in FIG. 3, the arm 75 firstly engages and then lifts the clutch ring 49. At the same time the resilient pawl or finger 83 will contact the periphery of the wormwheel 35 as the arm 75 of the lifting jack 72 is pivoted upwardly but will be pushed back by the wormwheel 35 due to its resilient construction. As the lifting jack 72 reaches its manual position in which the clutch ring 49 has been fully lifted, as shown in FIG. 3, the finger or pawl 83 will have cleared the periphery of the wormwheel 35 which will enable it to straighten along its length with its finger stud 84 resting on the top of the wormwheel surface. In this position release of the hand lever 62 will enable the lever to return to its original position under the force of its return spring 80 due to the lost motion provided by the two flats 70, 71 on the shaft 63 operating in the D-shape bore 74 as provided in the lifting jack 72 by means of the mounting of the Mills pin 79 across the bore 78 in the lifting jack. The finger or pawl 83 now retains the clutch member 26 in its uppermost or manual position until such time as the energisation of the motor 27 causes the wormwheel 35 to rotate in one direction or the other at which time the friction between the finger or pawl 83 and the surface of the wormwheel 35 will cause the stud 84 at the lower part of the finger or pawl 83 to move sideways due to its resilient construction. When this occurs the clutch ring or sleeve 49 will be moved downwardly by the clutch spring 54 which by its engagement with arm 75 will therefore return the lifting jack 72 also to its original position.

The hand lever 62 as its extends from the wall 65 of the casing ll of the actuator may be provided with a plate 85 formed with a circumferentially extending slot (not shown) in which a retaining screw 86 is located and attached to the wall 65 of the casing so as to form a stop limiting the movement of the hand lever 62 from its power position to its manual position.

If desired, the plate mechanism 85 attached to the hand lever 62 externally of the actuator casing It may be modified to provide a mechanism for locking the lever in either the hand and/or the power position. For example, the casing wall 65 surrounding the hand lever 62 may be provided with an abutment or extension which will permit a locking member to be inserted in either end of the slot in the hand lever plate in the two positions of the hand lever 62. The locking member will therefore engage or abut the edge of the casing extension to prevent movement of the plate 85 and thereby the hand lever 62 until the locking member is removed.

Although a spring finger or pawl 83 has been described it will, of course. be understood that the pawl or finger may be in the form ofa rigid member pivotally mounted on the lifting jack 72 and spring urged to its operative vertical position.

The output shaft 14 of the actuator is provided with a further worm 87 keyed thereto and drivably connected with a wormwheel 88 on a lower shaft 89 extending through the casing into the control unit housing. This lower shaft is rotatably coupled with a mccha nism for operating ancillary apparatus such as limit control switches for de-energising the actuator motor 27.

The clutch member 26 ensures that the valve cannot be simultaneously operated by both the manual and power devices and the finger or pawl assembly 83 enables the control of the actuator to be assumed immediately by the motor 27 whenever the actuator is power operated.

The actuator casing 11 is completed by an output 90 for connecting a housing thereto for the electrical supply and other control circuits.

The actuator construction and in particular the handlauto mechanism has been greatly simplified without loss of efficiency and this more simple construction not only assists production but enables a cheaper actuator to be manufactured.

In a modified embodiment of the hand/auto mechanism the cam surface is formed on the arm of the lifting jack. This modified embodiment is shown in FIG. 4 and as before the inner end of the hand lever shaft 63 is provided with two adjacent flats 70, 71 machined on its circumference at a predetermined angle one to the other.

A lifting jack 9] having an arm 92 is located on the machined end of the hand lever shaft 63 and is pro vided with a D-shaped hole 93 whereby the two flats 70, 71 on the shaft 63 provide the necessary turning movement to the jack while the angular relative positioning of the flats allows lost motion to take place between the shaft 63 and the lifting jack 9!.

The arm 92 of the liftingjack 91 extends inwardly of the actuator casing towards the clutch ring 49 and its upper inner end has a sloped or curved cam surface 94 which engages with the radiused underside 95 of the clutch ring or sleeve 49. The cam surface 94 is so sloped that the resultant force on the clutch ring or sleeve 49 is always at a constant angle relative to the centre line of the clutch ring or sleeve and is always within the length of the clutch members or keys as the clutch ring is lifted by the jack 91.

The lower surface of the lifting jack 9] is cut away at 96 and is formed with a hole 97 drilled therein for receiving a fulcrum pin 98 which extends forwardly of the front face 99 of the cut away portion of the lifting jack 91. A downwardly extending finger or pawl 100 is attached to the front end of the fulcrum pin 98 which is rotatably mounted in the drilled hole 97. Between the finger or pawl I00 and the front surface 99 of the cutaway portion of the lifting jack 9] there is provided a pair of springs 10!, 102 which are located around the fulcrum pin 98. The from spring 101 which abuts the finger or pawl I is a helical compression spring which urges the finger or pawl I00 forwardly with the fulcrum pin against a circlip I03 which is mounted on the fulcrum pin 98 and engages a rear surface portion I04 of the lifting jack. The rear spring I02 extends around the fulcrum pin 98 and is formed with two end leg portions 105,106 which extend around the pin 98 and then downwardly to abut against the opposite surfaces of a pin I07 extending from the front face 99 of the cutaway portion of the lifting jack and a lower extension l08 to the finger or pawl I00. The second spring I02 therefore acts to maintain the finger or pawl 100 normally in a vertical position but the spring 102 by its resilient nature allows the pawl or finger I00 to rotate sideways with the fulcrum about the axis of the pin 98. The two springs I0], I02 on the fulcrum pin 98 are separated by a washer 109 to prevent jamming or the winding of one spring on the other.

The lower front portion of the finger or pawl I00 is curved or cut away for engaging the periphery of the wormwheel 35 as the clutch ring or sleeve 49 is lifted by the jack 9I.

The hand lever assembly as it extends through the casing of the actuator is constructed in the manner previously described. When the hand lever is operated the lifting jack 91 is moved so as to engage the curved cam surface 94 of the arm 92 with the radiused corner 95 of the clutch ring 49. As the clutch ring is lifted by the jack the point of contact will move whilst ensuring that the resultant force on the ring is always at a constant angle relative to the centre line of the clutch ring. At the same time the finger or pawl I00 attached to the fulcrum pin 98 will contact the periphery of the wormwheel and as the lifting jack 9] is pivoted upwardly by the hand lever 62 the pawl or finger I00 will be pushed back by the wormwheel 35 against the compression spring IOI. As the liftingjack 9I reaches its manual position in which the clutch ring or sleeve 49 has been fully lifted. the finger or pawl I00 will have cleared the wormwheel 35 and will be able to spring forwardly again so as to rest on top of the surface of the wormwheel 35. In this position no further movement of the jack 9I can now take place because of the retaining stop in the slot on the lever plate 86. In this position the operator will release the lever 62 which will then return to its original position under the force of its spring 80 and because of the lost motion in the D hole 93 in the lifting jack as hereinbefore described. The finger or pawl I00 now retains the clutch ring 49 in its upper or manual position until such tme that the energisation of the motor 27 causes the wormwheel 35 to rotate in one direction or the other at which time the friction between the finger or pawl I00 and the wormwheel surface will cause the finger or pawl I00 to be moved sideways about its fulcrum pin 98 and against the action of the second spring I02 on the fulcrum pin. The pawl or finger 100 will move sideways until it becomes free from the surface of the wormwheel 35 and when this occurs the lifting jack 91 will be moved downwardly about shaft 63 to its original position as shown in FIG. 4 by the downward force of the clutch spring 54. As the lifting jack 91 returns to its original position the finger or pawl I00 will also be returned to its upright position by the action of the second spring 102 on the fulcrum pin 98.

As previously mentioned the finger or pawl I00 is provided with a rearwardly extending pin I08 engaged at its opposite sides by the two legs I05, 106 ofthe sec ond spring 102 on the main fulcrum pin 98. This centralising spring 102 may be modified as an extension of the finger or pawl I00 which may be formed as a curved member extending from the front end of the fulcrum pin 98 downwardly and then rearwardly between the legs [05,106 of the second spring I02. In yet another modified arrangement the fulcrum pin 98 may be formed integrally with the finger or pawl I00 and the centralising pin I08 in the form of a U-shaped member.

I claim:

I. In a drive mechanism which has an output shaft, power means for rotating the output shaft, and means for manually rotating the output shaft, an annular clutch member non-rotatably mounted on the output shaft and having bearing surfaces slideable axially thereon operably connecting the output shaft to said manually rotating means and said power means, a clutch ring on said clutch member, a clutch actuator associated with said clutch member and engaging said clutch ring, resilient means for urging the clutch mem her away from the manually rotating means, said actuator being rotatable about an axis which is perpendicular to the axis of the clutch member for moving said clutch member axially against said resilient means for operably connecting the output shaft to the manually means, one of the engaging surfaces of the clutch ring and actuator being shaped as a cam surface sloping towards the axis of said shaft whereby the force exerted on the clutch member against said resilient means by the actuator as it is rotated is applied at a constant angle relative to the center line ofthe clutch member and always intereacts the shaft within the length of said bearing surfaces so as to prevent jamming between the clutch member and the output shaft.

2. In a' drive mechanism as claimed in claim I wherein said manually operating means comprises a handwheel and said actuator comprises means for holding the clutch member in driving engagement with the handwheel.

3. In a drive mechanism as claimed in claim I wherein said resilient means moves said clutch member axially into driving engagement with said power means when said actuator is inoperative.

4. In a drive mechanism as claimed in claim 3 comprising a wormwheel mounted on said output shaft and freely rotatable relatively thereto, said wormwheel being drivably connected with said power means for operation thereby upon energization of said power means and said clutch member is moved into engagement with said wormwheel by said resilient means.

5. In a drive mechanism as in claim I wherein the engaging surface of said clutch ring is a frusto-conically shaped surface and said clutch actuator has an arm which moves over the frusto-conically shaped surface as the actuator is rotated and moves the clutch ring. and resilient means for supporting the clutch ring in its moved position.

6. In a drive mechanism as claimed in claim I comprising a wormwheel mounted on said output shaft and freely rotatable relative thereto, said wormwheel being drivingly connected with said power means for operation thereby upon energization of said power means, and said resilient means for supporting the clutch ring is a pawl which is engageable with the surface of the 9 wormwheel to hold the clutch member in driving engagement with the manually operating means.

7. In a drive mechanism as claimed in claim 6, wherein the pawl is a resilient stud mounted in an arm extending from the actuator for engaging the clutch ring.

8. In a drive mechanism as claimed in claim 6, wherein the pawl is pivotally mounted on the actuator and comprises a rigid member spring urged to a vertical position for engaging the surface of said wormwheel.

9. In a drive mechanism as claimed in claim 1 wherein the engaging surface of the actuator is a tOl't 

1. In a drive mechanism which has an output shaft, power means for rotating the output shaft, and means for manually rotating the output shaft, an annular clutch member non-rotatably mounted on the output shaft and having bearing surfaces slideable axially thereon operably connecting the output shaft to said manually rotating means and said power means, a clutch ring on said clutch member, a clutch actuator associated with said clutch member and engaging said clutch ring, resilient means for urging the clutch member away from the manually rotating means, said actuator being rotatable about an axis which is perpendicular to the axis of the clutch member for moving said clutch member axially against said resilient means for operably connecting the output shaft to the manually means, one of the engaging surfaces of the clutch ring and actuator being shaped as a cam surface sloping towards the axis of said shaft whereby the force exerted on the clutch member against said resilient means by the actuator as it is rotated is applied at a constant angle relative to the center line of the clutch member and always intereacts the shaft within the length of said bearing surfaces so as to prevent jamming between the clutch member and the output shaft.
 2. In a drive mechanism as claimed in claim 1 wherein said manually operating means comprises a handwheel and said actuator comprises means for holding the clutch member in driving engagement with the handwheel.
 3. In a drive mechanism as claimed in claim 1 wherein said resilient means moves said clutch member axially into driving engagement with said power means when said actuator is inoperative.
 4. In a drive mechanism as claimed in claim 3 comprising a wormwheel mounted on said output shaft and freely rotatable relatively thereto, said wormwheel being drivably connected with said power means for operation thereby upon energization of said power means and said clutch member is moved into engagement with said wormwheel by said resilient means.
 5. In a drive mechanism as in claim 1 wherein the engaging surface of said clutch ring is a frusto-conically shaped surface and said clutch actuator has an arm which moves over the frusto-conically shaped surface as the actuator is rotated and moves the clutch ring, and resilient means for supporting the clutch ring in its moved position.
 6. In a drive mechanism as claimed in claim 1 comprising a wormwheel mounted on said output shaft and freely rotatable relative thereto, said wormwheel being drivingly connected with said power means for operation thereby upon energization of said power means, and said resilient means for supporting the clutch ring is a pawl which is engageable with the surface of the wormwheel to hold the clutch member in driving engagement with the manually operating means.
 7. In a drive mechanism as claimed in claim 6, wherein the pawl is a resilient stud mounted in an arm extending from the actuator for engaging the clutch ring.
 8. In a drive mechanism as claimed in claim 6, wherein the pawl is pivotally mounted on the actuator and comprises a rigid member spring urged to a vertical position for engaging the surface of said wormwheel.
 9. In a drive mechanism as claimed in claim 1 wherein the engaging surface of the actuator is a curved cam surface and the engaging surface of the clutch ring is a radiused underside edge thereof.
 10. In a drive mechanism as claimed in claim 1 having a handle extending through its casing, the actuator is mounted on the inner end of the handle, the inner end of said handle comprising a shaft portion having two adjacent flats formed thereon for engagement within a bore in said actuator whereby a lost motion connection is provided between said handle and actuator. 